1. Field of the Invention
The present invention pertains to well production logging tools and more particularly to well production logging tools that measure the flow of fluids into the well and are capable of determining the flow of various fluids within the well.
2. Related Prior Art
There are many methods and apparatus for measuring the fluid flow within a producing oil well. Some of these use ultra sound to determine interfaces and travel time within the fluid. Some representative patents of the state of the art production logging tools are as follows.
U.S. Pat. No. 3,454,085, titled "Well Installation with Plural Flow Meters", issued to J. H. Bostock relates to a well installation providing fluid flow communication between the earth surface and one or more earth formations penetrated by a well bore by means of a flow conductor which extends through the well bore. The flow conductor has vertically spaced ports between barriers which close the well bore about the flow conductor between each pair of such earth formations. The ports provide communication between the flow conductor and the earth formations. Flow meters mounted on the flow conductor are used to determine the rate of flow of fluid in the flow conductor above or below each port so that the rate of flow of fluids between each such earth formation and the flow conductor can be determined.
U.S. Pat. No. 5,138,585, titled "Method for Fluid Identification and Evaluation Within Wellbores Using Ultrasonic Scanning" issued to Jorg A. Angehru and Charles F. Magnani, relates to a method for using data from a borehole televiewer in an active well to determine flow properties. The method discussed in this patent involves determining the wall effects from the data, and factoring out the wall effects from the data to determine the fluid properties.
U.S. Pat. No. 3,603,145, titled "Monitoring Fluids in a Borehole" issued to Billy P. Morris, relates to a method and apparatus for monitoring flow and character of fluids in a borehole penetrating subterranean formations. This patent describes an apparatus that transmits acoustic energy through the borehole fluids between transducers in a down-hole tool and discriminates intelligence bits from the acoustic energy arriving at the transducer serving as receiver. A portion of the acoustic energy is transmitted upstream and a portion of the acoustic energy is transmitted downstream. In one embodiment described in this patent, intermittent acoustic energy is employed and the intelligence bits are, respectively, the travel time downstream and the travel time upstream. This method purports to afford information as to the difference in the respective travel times which is related to velocity of the flow of the fluids and the average travel time which is related to the density of the fluids. In another embodiment described in this patent, intermittent or continuous acoustic energy is employed and the intelligence bits are respectively, apparent frequency and amplitude. The apparent frequency allegedly affords information as to frequency shift which is related to velocity of fluid flow. The amplitude is related to fluid density. Also disclosed are specific details of generating functions related to the received acoustic energy, and to the logging of the intelligence information with respect to depth.
U.S. Pat. No. 3,776,032, titled "Method and Apparatus for Detecting an Inflow of Fluid into a Well", issued to Charles B. Vogel, relates to a method and apparatus for detecting an inflow of fluid into a well during rotary drilling of the well. An inflow of gas is detected by an acoustic device and an inflow of water is detected by a resistivity device. The resulting information is transmitted to the surface by pressure pulses produced in the drilling fluid circulated during drilling.
In current practice, measurements are made in the central portion of the wellbore cross-section. These measurements are such as of spinner rotation rate, fluid density and dielectric constant. This data is then interpreted in an attempt to determine the flow rate at any point along the borehole. Influx (or exit) rate over any interval is then determined by subtracting the flowrates at the two end of the interval. However, in deviated and horizontal wells with multiphase flow, and also in some vertical wells such methods frequently give erroneous results due to the complex flow patterns within the wellbore giving non-representative readings. All prior art production logging measurements are made in these complex flow regimes in the central area of the borehole and yield non-representative results, or have other severe limitations.